Vascular systems are essential for the growth and development of most animals larger than a few[unreadable] centimeters in size because diffusion is inadequate. Members of the Cnidaria, one of the earliest animal[unreadable] phyla, exhibit primitive vascular systems. Colonial cnidarians consist of polyps connected to one another by[unreadable] a common vascular system that integrates colony-wide behavior. Polyps gather and distribute food by[unreadable] pumping it through the gastrovascular system. Vascular transport is sensitive to food availability, oxygen[unreadable] tension and other environmental factors, and vascular architecture. Colony form is inextricably linked to[unreadable] gastrovascular transport and, consequently, plasticity of colony form is considerable and can be adaptive.[unreadable] The goal of the proposed project is to determine if mechanisms regulating vascular development and its[unreadable] plasticity in hydrozoans represent shared primitive characters of metazoans. This objective will be met by[unreadable] testing the following hypotheses: (1) Hydrozoan colony form is plastic in response to oxygen tension (pO2),[unreadable] and manipulations of seawater viscosity that alter shear stress on endodermal cells of stolons. (2) Rates of[unreadable] polyp formation, stolon branching and mitosis of stolon endodermal cells differ with the length and[unreadable] architecture of the stolon on which they reside. (3) Mitotic rates of endodermal cells lining the lumen of[unreadable] stolons increase in response to hypoxia and vascular shear stress. (4) Expression of HIF-1 alpha, VEGF,[unreadable] and matrix metalloproteinase gene homologues increase in response to hypoxia and vascular shear stress[unreadable] and are, therefore, consistent with roles regulating growth and branching of stolons. If vascular development[unreadable] of hydrozoans and vertebrates are regulated by the same mechanisms, the long-term goal is to develop[unreadable] colonial hydrozoans as alternative and complementary models to those of vertebrates for studies of vascular[unreadable] function and its pathologies.[unreadable] Indeed, the relevance of this research to public health lies in the potential for hydrozoan gastrovascular[unreadable] systems to serve as models for studies of human vascular function because of evolutionary conservation of[unreadable] developmental signaling pathways triggered by physiological responses. The practical benefits of utilizing[unreadable] them as models include in vivo experimentation, low cost, clonal replication, and few ethical constraints.